The present invention relates to an electrophoretic device, a driving method thereof, and an electronic apparatus provided therewith, and more in particular, it relates to an electrophoretic device excellent in visibility and contrast characteristic and having consistent display maintaining characteristic for a long time, a driving method thereof, and an electronic apparatus provided therewith.
Conventional electrophoretic display devices utilizing changes in a distribution condition of electrophoretic particles dispersed in dispersion medium by applying the voltage between a pair of electrodes facing each other including one in which electrophoretic dispersive solution containing dispersion medium and electrophoretic particles is placed in an area which is provided, for example, on a base body and demarcated by bulkheads, and is used as an electrophoretic layer, and one in which a micro capsule accommodating electrophoretic dispersive solution therein is used in place of provision of bulkheads.
Generally speaking, if the above electrophoretic device is used for the electrophoretic display device, desired display is performed by mixing dye in the dispersion medium, and by the contrast of the display color of the dispersion medium with the dye mixed therein and the display color of electrophoretic particles.
However, in some combinations of the display color of the dispersion medium with the display color of the electrophoretic particles, the display color of the electrophoretic particles can be observed by transmitting the colored dispersion medium if electrophoretic particles are located opposite to observation side when viewed from the observation side of the display device, and in particular, the display color of the electrophoretic particles is dark, for example, blackish, its trend becomes conspicuous, and the electrophoretic display device has not been sufficient in visibility, contrast characteristic, etc.
If the electrophoretic device is used for a display device such as an electronic paper which must maintain the display content for a long time, the distribution condition of electrophoretic particles in electrophoretic dispersive solution corresponding to the display content must be maintained for a long time.
The present invention is thus made paying attention to unsolved problems, and the object of the present invention is to provide an electrophoretic device which is capable of improving the visibility and the contrast characteristic and maintaining the distribution condition of electrophoretic particles for a long time, and suitable for a display device, and a method for driving the electrophoretic device, and an electronic apparatus having the electrophoretic device.
In order to achieve the above object, the electrophoretic device of the present invention is characterized in that it comprises the electrophoretic layer containing the dispersion medium and the electrophoretic particles dispersed in this dispersion medium with the position of the electrophoretic particles controlled according to the electric potential applied to the electrodes, and the dispersion medium is mixture of a plurality of substances, and the mutual solubility of these substances is low.
The electrophoretic device in which an electrophoretic layer containing the dispersion medium and electrophoretic particles dispersed in the dispersion medium is disposed between a pair of electrodes is characterized in that the dispersion medium is mixture of a plurality of substances, and the mutual solubility of these substances is low.
Here in the above electrophoretic device, at least one of the plurality of substances is preferably non-fluid at normal temperature, and fluid at non-normal temperature.
In the above electrophoretic device, the plurality of substances are preferably different from each other in the refractive index thereof.
In the above electrophoretic device, the dispersion medium is preferably mixture of at least one kind of substance selected among long chain alcohols including hexadecyl alcohol and octadecyl alcohol, phenols including phenol and cresol, aromatic ketones including benzophenone and benzaldehyde, decanes, and dodecanes, with at least one kind of substance selected among paraffin, waxes, or waxes mainly consisting thereof, and saturated hydrocarbons.
In the above electrophoretic device, the dispersion medium may contain dispersing agent.
In the above electrophoretic device, the dispersion medium with the electrophoretic particles dispersed therein may be sealed in an area demarcated by the bulkhead provided between the electrodes.
In the above electrophoretic device, the dispersion medium with the electrophoretic particles dispersed therein may be contained in a micro capsule, and sealed between the electrodes, and the micro capsule is preferably disposed uniform in thickness and flat between the electrodes.
The above electrophoretic device preferably comprises a heating means for heating the dispersion medium.
The above electrophoretic device may comprise a cooling means for cooling the dispersion medium.
The electrophoretic device preferably applies the electric potential to the electrodes with the electrophoretic layer in a non-normal temperature condition.
The driving method of the electrophoretic device of the present invention is characterized in that the electrophoretic layer contains the dispersion medium and electrophoretic particles dispersed in the dispersion medium, and the position of the electrophoretic particles is controlled according to the electric potential applied to the electrodes, and that the dispersion medium is formed of mixtures which consist of a plurality of substances and is fluid at the electrophoretically operational temperature in the electrophoretic layer while the dispersion medium is formed by the mixture which is optically opaque solid at the temperature lower than the electrophoretically operational temperature, and the electric potential is applied to the electrodes with the temperature of the electrophoretic layer is set to be the electrophoretically operational temperature.
The method for driving the electrophoretic device of the present invention in which the electrophoretic layer containing the dispersion medium and the electrophoretic particles dispersed in the dispersion medium is disposed between a pair of electrodes is characterized in that the dispersion medium is formed of a mixture of a plurality of substances which is fluid at the electrophoretically operational temperature for performing the electrophoretic operation in the electrophoretic layer, and optically opaque solid at the temperature lower than the electrophoretically operational temperature, and the electric potential is applied to the electrodes with the temperature of the electrophoretic layer set to be the electrophoretic operational temperature.
In the driving method of the above electrophoretic device and the above electrophoretic device, the mixture of a plurality of substances is used as the dispersion medium, and the mixture of low mutual solubility of the plurality of substances is used. The mutual solubility of the plurality of substances forming the dispersion medium is small, and the liquid does not become homogeneous, and thus, the transmissivity is degraded. For example, if the electrophoretic particles are located on the distal side from, for example, the observation side, the electrophoretic particles cannot be visually recognized from the observation side. Thus, the contrast of the electrophoretic particles with the dispersion medium can be ensured, and the visibility can be improved.
At least one of the plurality of substances constituting the dispersion medium is non-fluid at the normal temperature and is fluid at the non-normal temperature, and as a result, the dispersion medium is non-fluid at the normal temperature. Thus, the position of the electrophoretic particles at this time can be maintained. Therefore, if used as the electrophoretic display device, the dispersion medium is heated by, for example, the heating means, and the electrophoretic particles are electrophoretically operated in a non-normal temperature to perform a desired display. After that, the dispersion medium is cooled by a cooling means not shown in the figure to be maintained at the normal temperature, and the display content can be maintained thereby.
The normal temperature here means the temperature of the environment in which the electrophoretic device in the display state is placed if the electrophoretic device of the present invention is used as the display device.
The composition of the dispersion medium can be appropriately adjusted according to the temperature of the environment in which the electrophoretic device in the display state is placed. In addition, as described below, the normal temperature generally corresponds to the room temperature.
The light scattering intensity is increased by consisting the dispersion medium of a plurality of substances much different in the refractive index, and the visibility and the contrast characteristic can be improved more as the difference in the refractive index is larger.
Dispersibility of the electrophoretic particles in the dispersion medium can be improved by mixing the dispersing agent in the dispersion medium, the zeta potential self-excited by the electrophoretic particles can be increased, the electrophoretic speed of the electrophoretic particles in applying the voltage can be increased, and as a result, the response speed can be increased.
The electronic apparatus of the present invention is characterized in that the above electrophoretic device is provided as the display body in the electronic apparatus comprising the display body and the driving circuit for feeding the drive signal to the display body.
This electronic apparatus can ensure the contrast of electrophoretic particles with the dispersion medium by providing the electrophoretic device as a display body, and can improve the visibility.